162 STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



its cells are seen to lie, sometimes singly, and sometimes in clusters of 

 two, three, or four, in cavities excavated in the intercellular substance. 

 These occur at very variable distances ; for in some instances they are 

 packed together as closely as the cells of a vegetable parenchyma (Fig. 

 38); whilst in others the principal mass is composed of intercellular 

 substance, through which the cells are interspersed at wide intervals. 

 From the various appearances which may be observed in the same car- 

 tilage, at different stages of its growth, it would appear that the compo- 

 nent' cells multiply by the doubling process already described ( 212) ; 

 that they then separate from one another, each of them drawing towards 

 itself (as it were) an envelope of intercellular substance ; and that, by 

 the repetition of the same process, the number of cells in the cartilage 

 may be indefinitely multiplied. 



267. Various stages of this history are shown in the accompanying 

 figure (Fig. 39), which is taken from a section of the cartilaginous bran- 

 chial ray of the larva or tadpole of the Rana esculenta, or Edible Frog. 

 In the centre of the figure are shown three separate cells, which have 

 evidently been at one time in closer proximity with each other. In one 

 of these cells, the nucleus is seen to be developing two new cells in its 

 interior ; and a continuation of this process would give rise to the appear- 

 ance shown at 5, where two cells are shown in close contact, being evi- 

 dently the offspring of the same parent. Now if each of these cells in 

 like manner developes two others within itself, a cluster of four will be 

 developed, as shown at a ; and after a time, intercellular substance being 



Fig. 39. 



Section of the Branchial cartilage of Tadpole; a, group of four cells, separating from each other; b, pair 

 of cells in apposition; c, c, nuclei of cartilage cells; d, cavity containing three cells. 



accumulated around each, their walls will separate, and they will acquire 

 the character of distinct cells. It would seem as if, in other cases, one 

 of the first pair of cells developes another pair in its interior, whilst the 

 other (from some unknown cause), does not at once proceed to do so ; 

 and thus only three cartilage-cells instead of four are clustered together 

 in the cavity, as seen at d. 



268. The primitive cellular organization now described is retained in 

 some Cartilages through the whole duration of their existence. This is 

 the case, for example, in most of the articular cartilages of joints ; in 

 the cartilaginous portion of the septum narium, in the cartilages of the 

 alae and point of the nose, in the semilunar cartilages of the eyelids ; in 

 the cartilages of the larynx (with the exception of the epiglottis), the 



